Thorsteinn,
one of my professors told me "if you think about it, and it seems practical, the chances that they may have come up with something like it back then is almost proven."
I seriously doubt mantles and such were "invented" in the 12/13th centuries. I just think they blossomed and became in vogue in the 13th and 14th centuries. Also, during the 9th century, the planet was in a state of a mini-ice age, sorry, my geography/geology sucks but that's the term I know it as. So the layers make more sense. Beyond that, even in the blistering cold, a cold helmet is definitely not a good thing. So again, I think it's safe to suppose they wore some kind of helmet protection, those that actually could afford a helmet in the 9th century
btw, I also wanted to congratulate you on your kit. For fighting in the SCA during the pre 11th century, "you sure done good kid, ya sure done good." - quoting the Duke.